Most original, exciting, fresh, mindblowing? Doesn't have to be theory, non-fiction, or even leftist. I just wanna get to know more exciting books.
My own answers:
Non-fiction: Debt - The Last 5000 Years and A Paradise Built In Hell were paradigm shifts for me, in a great way.
Fiction: Gonna have to be The Trojan War Will Not Take Place. Yes it's a play from 1935 but it was more interesting for me than many more current books, and the anti-war message is unfortunately still fresh.
A Polish book "Ostre cięcie. Jak niszczono polską kolej". A book on how nearly all the governments (but especially the neoliberal ghouls) nearly completely dismantled Polish rail.